MPEG-4 as defined in the MPEG-4 Audio standard ISO/IEC 14496-3:2001 and the MPEG-4 Systems standard 14496-1:2001 facilitates a wide variety of applications by supporting the representation of audio objects. For the combination of the audio objects additional information—the so-called scene description—determines the placement in space and time and is transmitted together with the coded audio objects.
For playback the audio objects are decoded separately and composed using the scene description in order to prepare a single soundtrack, which is then played to the listener.
For efficiency, the MPEG-4 Systems standard ISO/IEC 14496-1:2001 defines a way to encode the scene description in a binary representation, the so-called Binary Format for Scene Description (BIFS). Correspondingly, audio scenes are described using so-called AudioBIFS.
A scene description is structured hierarchically and can be represented as a graph, wherein leaf-nodes of the graph form the separate objects and the other nodes describes the processing, e.g. positioning, scaling, effects etc. The appearance and behavior of the separate objects can be controlled using parameters within the scene description nodes.